Motion sickness is a debilitating condition that affects a wide range of individuals in both daily life and in pathological conditions. While it is widely seen in many clinical settings, it remains difficult to objectively evaluate and treat. Recent work by our group has found a connection between decreases in brain blood flow and the development of nausea. Based on this and other research, the question arises as to what role does decreased brain blood flow play in the development of motion sickness. The overall goal of this work is to determine the relationship between brain blood flow and the development of motion sickness. To answer this question we are proposing the following specific aims: 1) Determine if decreases in brain blood flow can accurately predict the onset of motion sickness; 2) Determine if maintaining end tidal CO2 during a motion stimulus eliminates the reduction in cerebral blood flow due to increased ventilation and extends time to symptoms or eliminates the development of motion sickness. To achieve this goal we will use off vertical axis rotation at two rotation speeds, one which has been shown to be very nauseogenic and one which is easily tolerated. We can compare the response of these two paradigms to determine if brain blood flow decreases prior to motion sickness symptoms. In addition we can add inspired CO2 to maintain arterial CO2 and improve brain blood flow during rotation. The findings of this work could translate into significant clinical and research advancements. Using brain blood flow during desensitization training could reduce aversive events and greatly enhance and broaden the clinical applications of motion sickness treatments. The development of an objective measure of motion sickness would allow for better understanding of the mechanisms. PUBLIC HEALTH RELEVANCE: The goal of this research is to understand the relationship between brain blood flow and the development of motion sickness. By understanding how reductions in cerebral blood flow are related to the development of nausea, new diagnostic and treatment methods may be developed.